Current television and or radio services often provide pay-per-use or conditional access to program content. Customers who do not pay for the privilege of receiving the content are prevented from receiving the signals by encoding, and often by encrypting, the signals which contain the content. The term “encoding” is used herein for encoding, scrambling, and encrypting, and “decoding” for decoding, descrambling, and decryption. Paying customers receive a decoding key so that they may decode the encoded content for use.
Unfortunately, some persons may receive the encoded signal and extract the key, either on- or off-line, and may thereby avoid paying the fee for use of the content. FIG. 1 is a simplified block diagram of a cable television system 10 including one subscriber. In the system of FIG. 1, video or music content 1, which is to be made available as pay-per-view, is applied to an encoder 12a. Encoder 12a encodes the content with the aid of a key produced by a key generator 14a, which is applied to an input port 12ai, to produce encoded first content. The encoded first content produced by encoder 12a is applied to a frequency upconverter 16a, which converts the frequency to a unique frequency range or channel, centered on a frequency f1. Second content 2, which is to be made available to all subscribers, is applied directly to a second frequency upconverter 16b, which converts the unencoded content to a second unique frequency range. System 10 of FIG. 1 includes other frequency upconverters and may include other encoders, such as encoder 12N, which encodes content N by means of a key, which may be the same key as that used for encoder 12a, or which may be a different key from a generator 14N, applied to its encoding input port 12Ni. The encoded output of encoder 14N is applied to an upconverter 16N for conversion to a frequency range fN, different from the other frequency ranges. The encoded and unencoded signals on frequencies f1, f2, . . . , fN are applied to a frequency-sensitive combiner 18, which combines the signals onto a single path, which is the system television transmission path or line 20 (which may be a coaxial cable or an optical fiber).
The many carriers at the various frequencies f1, f2, . . . , fN flow along the cable 20 toward the subscribers. It should be understood that each separate carrier frequency on the cable system 10 constitutes a single channel which carries only one content. At any given subscriber's location, a portion of the signal including carriers f1, f2, . . . , fN is removed from the transmission path 20, as by a directional coupler 22, and carried to the subscriber's location, designated 24 in FIG. 1. At the subscriber, the signal is made available either directly to a television receiver 26, or if the system carrier frequencies are different from conventional television carrier frequencies, or if decoding of content are desired, the signal is made available to the television receiver 26 by way of a receiver/decoder 30. Receiver/decoder 30 receives only one channel, so receives from the cable only one channel.
When the subscriber at location 24 wishes to view unrestricted content, the television receiver 26 or the receiver portion of receiver/decoder 30 is set to select the appropriate one of the frequency ranges flowing in transmission path 20 (the desired channel), and the content may be viewed or listened to without more.
If the subscriber wishes to use conditionally restricted content, the television receiver (or monitor) 26 or the receiver portion of receiver/decoder 30 is set to select the appropriate one of the frequency ranges flowing in transmission path 20. However, this is insufficient to allow the content to be used. In order to use the conditionally restricted content, the subscriber must obtain a suitable decoding key for use in operating the decoding algorithm at his receiver/decoder. Many methods of obtaining the key are known, such as purchase of a card in a bricks-and-mortar store. One known way to obtain a key is for the subscriber to use a telephone to call a service center affiliated with the cable company, identify himself and make the appropriate payment, and receive the key electronically over the transmission path 20 of FIG. 1.
Some persons may attempt to obtain the use of the conditionally restricted content by storing the encoded content in a memory associated with a computer, and using the processing power of the computer to attempt to determine the encoding key or algorithm. In FIG. 1, a sample of the signal received from the receiver/decoder 30 at location 24 is made available to a computer 34. Computer 34 may be used to store the key transmitted over path 20, the encoded signal received by the receiver portion of receiver/decoder 30, or both. With the key and or signal stored, it or they can be manipulated by computer algorithms to attempt to extract the encoding algorithm, key, or both. With that information available, the encrypted information content becomes available to the subscriber at location 24, notwithstanding that he has not paid for the content.
Improved methods are desired for protection of information against unauthorized use.